Chemical-mechanical polishing methods

Abstract

The polishing uniformity of a material on a substrate is improved by using a polishing method where an applied pressure on the backside of the substrate is changed during the polishing process. The method is especially useful for polishing thin material layers requiring precise control of polishing across the substrate, e.g., for TaSiN layers used in the formation of gate stacks and stacked capacitors.

What is claimed is:  
     
       1. A method of polishing a surface of a flexible wafer capable of having a convex and/or concave surface by chemical-mechanical polishing, said method comprising: 
       a) providing said wafer having first surface to be planarized and a second surface on an opposite side of said wafer from said first surface, said first surface having first and second regions,  
       b) providing a liquid polishing medium,  
       c) contacting said first surface with said liquid medium and a polishing member, and applying a first pressure against said second surface, and  
       d) maintaining the contact and applied pressure of step c) while providing movement between said wafer and polishing member, whereby a first portion material of said first surface is removed,  
       e) contacting said first surface with said liquid medium and polishing member, and applying a second pressure against said second surface, and  
       f) maintaining the contact and applied pressure of step e) while providing movement between said wafer and polishing member, whereby a second portion material of said first surface is removed,  
       said first and second pressures being sufficiently different from each other whereby a ratio of material removal rate in step (f) in said first region to a material removal rate in step (f) in said second region is different compared to a corresponding material removal rate ratio for said regions in step (d). 
     
     
       2. The method of  claim 1  wherein said first surface contains at least one transition metal nitride feature. 
     
     
       3. The method of  claim 2  wherein said transition metal is selected from the group consisting of tantalum and tungsten. 
     
     
       4. The method of  claim 3  wherein said transition metal is tantalum. 
     
     
       5. The method of  claim 4  wherein said nitride feature is a TaSiN feature. 
     
     
       6. The method of  claim 1  wherein said liquid medium contains a particulate abrasive. 
     
     
       7. The method of  claim 6  wherein said abrasive is an alumina. 
     
     
       8. The method of  claim 7  wherein said abrasive is a gamma alumina. 
     
     
       9. The method of  claim 1  wherein said liquid medium comprises is an aqueous medium. 
     
     
       10. The method of  claim 9  wherein said liquid medium has a pH of about 4.5-5.5. 
     
     
       11. The method of  claim 10  wherein said liquid medium has a pH of about 5.2. 
     
     
       12. The method of  claim 11  wherein said liquid medium further comprises a mineral acid. 
     
     
       13. The method of  claim 9  wherein said liquid medium comprises and oxidizer. 
     
     
       14. The method of  claim 13  wherein said liquid medium further comprises hydrogen peroxide. 
     
     
       15. The method of  claim 1  wherein said wafer comprises a silicon nitride region and step (f) is conducted until at least a portion of said silicon nitride region is exposed. 
     
     
       16. The method of  claim 1  wherein said first and second fluid pressures cause different amounts of flexion in said wafer in steps (d) and (f) respectively. 
     
     
       17. The method of  claim 1  wherein said wafer is maintained continuously in contact with said liquid medium from step (c) through step (f).